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can a GPS antenna cable length be reduced?

rv8ch

Well Known Member
Patron
Does anyone know if it's "possible" to reduce the GPS antenna length?

I have one from GRT like this, but with a much longer cable:

MK-76-antenna.jpg


I'll be mounting my antenna on the glareshield, so I don't need the extra 10 feet of cable. Thanks for any tips.
 
Yes, you may shorten a GPS antenna cable if you have the proper tools to install a new connector.
 
Mel is completely correct - but after you source the fitting and the crimper, you might find that bundling up the excess cable underneath the glareshield with a couple of zip ties is mighty attractive.....
 
Although not recommended, you can cut and splice IF you understand how to prep and dress the cable, and are an expert soldering technician. If you don?t have experience with shielded cable, not the time to learn.
 
Depends on the application.

The installation instructions for the WAAS GPS that comes with the Stratus ESG transponder implicitly limits how short the coax can be (ten feet in some instances). It states too short a lead on the active GPS receiver will overload the transponder and degrade performance.

So yes, why not just bundle up the coax and zip tie it to under-structure.
 
I have the tools to install MCX, SMA and BNC connectors on this type of small RG174 coax used with these antennas. But JonJay nailed it. The small components are hard to work with and 9 out of 10 of them require soldering with a super fine tipped soldering iron in a small cavity. You have better have a magnifier glass and zero hand shake (no coffee for you that day). Since these are active antennas a bad connector installation could short and fry something expensive. If you had a BNC end it would be easier as there are double crimp connector options not requiring soldering. But yours appears to be MCX.

Sam hit on another very good point. The designers of the components use an assumption of a minimum amount of impedence loss in a typical installation. To reduce the db loss with a shorter run on a lead can cook components. For example, when installing UAT out ADS-B units Freeflight requires a minimum loss so I have gone so far as to use RG 58 and even RG174 coax lead to the ADS-B transponder type antenna in order to meet the minimum loss rather than coiling up a longer run of higher quality RG400 coax required to achieve the same loss. Interestingly the Garmin GDL-82 doesn't specify a minimum loss value and so I keep those coax runs short. As for your replacement item, I can't answer as to whether the GPS antenna designers need the full 10 feet of coax to meet any loss requirements.

In the end I always keep the as delivered length and neatly coil up the excess cable in a round loop with zip ties behind the panel and have never had any signal or performance issues.

Jim
 
"Does anyone know if it's "possible" to reduce the GPS antenna length? I have one from GRT like this, but with a much longer cable"

Good points from everyone. Perhaps you should contact GRT and ask them about cable length restrictions (maybe they'll even exchange it for one with a shorter cable). It also depends on your definition of "much longer". Do you want to go through the trouble to eliminate 9 inches of cable? 20"? At some point, it probably makes sense to shorten it rather than loop it and tie it up (pending the answer from GRT).
Yes, it's "possible". Should you? Maybe.
 
We supply our GPS antennas with a 15 feet cable. That is quite long.

We do not recommend that the cable be shortened in our case as the antenna contains an amplifier and the gain is matched to compensate for cable losses. So if you shorten the cable dramatically you will end up with too much signal at the GPS receiver. While this does not overdrive a modern receiver it does increase the noise level and as a result the GPS is less sensitive.

The long cable should not be an issue at all - the correct way to reduce the length is simple: In a convenient location coil the excess cable to you have a coil with about a foot or slightly less diameter now flatten the loop in the center and place a cable tie here so it stays that way. You now have something that roughly looks like a figure of eight. Keep it that way. The idea is to prevent sharp turns in the cable (which changes the cable impedance at that point). The remaining loops at the ends now have a graceful change of direction.

The reason why we want a flattened loop is to prevent the coil from acting as receiver for undesirable electrical interference and coupling this into your systems ground via the GPS. The flattened loop has less area (good) and you are creating two loops in a way that helps to cancel any induced signals.

Rainier
CEO MGL Avionics
 
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